This invention relates to a matrix array substrate for flat-panel display devices or the like and typically for liquid-crystal display devices.
Recently, flat-panel display devices such as liquid crystal display devices have been used as image display devices for personal computers, word processor-dedicated machines, television set, and the like because of their features that they are thin and light-weighted and consume a small electric power.
Active-matrix liquid crystal display (active-matrix LCD) devices in particular, which has pixel-switching elements arranged on each display pixel, enables to achieve good image quality without crosstalk between adjacent pixels. Because of these features, active matrix liquid crystal display devices are being earnestly investigated and developed.
In following, a light transmissive type device of the active-matrix LCD device is exemplified for explanation on its construction.
An active-matrix LCD device is comprised of a matrix array substrate (hereinafter referred as array substrate) and a counter substrate, which are closely opposed to each other with a predetermined gap, and of a liquid crystal layer held in the gap.
The array substrate has signal lines, for example in an upper-layer metal wiring pattern, and scanning lines, for example in a lower-layer metal wiring pattern. The signal and scanning lines are arranged in a latticework on an insulator substrate such as a glass plate, and are superimposed thorough an insulator film therebetween. On each rectangular patch defined by the signal and scanning lines, a pixel electrode is disposed and formed of a transparent electro conductive material such as Indium-doped tin oxide (ITO). At around each crossing of the signal and scanning lines, a pixel-switching element is disposed for controlling a respective pixel electrode. When the pixel-switching element is a thin film transistor (TFT), gate and signal electrodes of the TFT are respectively connected with scanning and signal lines a source electrode of the TFT is connected with a pixel electrode.
The counter substrate has a counter electrode formed of a transparent electro conductive material such as Indium-doped tin oxide (ITO), on an insulator substrate such as a glass plate. When to realize color display, color filter layers are formed on the substrate.
For securing a high quality of displaying on the active-matrix LCD device, each pixel electrode has to have a sufficient storage capacity (Cs). Thus, formerly, a storage capacitor line is arranged at between every two adjacent scanning lines as extended along the scanning lines. The storage capacitor lines are formed in a process step for forming the scanning lines. However, the storage capacitor causes decrease of an aperture ratio or light transmissive-area ratio of each pixel area.
For this reason, in a technique of the prior art, a metal float pattern for forming the storage capacity is provided for each pixel electrode on an area overlapping the scanning line and is connected to the pixel electrode through a contact hole.
In such construction, the pixel electrode may be short-circuited with the scanning line through a pinhole of a gate insulator film, which may be formed by a contamination particle at exposure process for forming resist pattern. Such short circuit causes decrease of yield of the array substrate, that is, ratio of salable product among all the produced.
Thus, there becomes increasingly prevailing a construction of forming the storage capacitor between the scanning line and an extended portion of the pixel electrode without forming the float pattern.
Meanwhile, the array substrate is completed after a plurality of film forming and patterning processes, and is usually subjected to inspection process at the time of completion. By the process, disconnection, short circuit and/or defect are detected if any.
At the inspection process, if pixel defects due to malfunction of pixel switching element is detected, the pixel defect is “repaired” by connecting the defected pixel electrode to a next pixel electrode, which neighbors the defected pixel electrode from a scanning-line-wise direction. A circuit for such repairing is referred as “tandem repair circuit”.
FIG. 6 shows a construction of an array substrate in the prior art.
A pixel electrode 5-1 is sandwiched between two consecutive scanning lines 11-1 and 11-2. One scanning line 11-2 among them is not for switching the pixel electrode 5-1 and is to be referred as “pre-scan-row scanning line”, which means a scanning line for scanning a next row of pixel electrodes in advance of scanning a row of pixel electrodes including the pixel electrode 5-1. An extended portion 51-1 extended from the pixel electrode 5-1 overlaps the pre-scan-row scanning line 11-2 to just cross over the scanning line 11-2. A tandem repair circuit 6 is disposed between the extended portion 51-1 and a “pre-scan-row electrode” 5-2 that is driven by the pre-scan-row scanning line 11-2. The tandem repair circuit 6 is for electrically connecting one pixel electrode 5-1 to the “pre-scan-row electrode” 5-2, if and only if a TFT for driving the pre-scan-row electrode 5-2 malfunctions.
The tandem repair circuit 6 is comprised of; first connector electrode 35 that is connected through a contact hole to the extended portion 51-1 extended from the pixel electrode 5-1; second connector electrode 36 connected with the pre-scan-row electrode 5-2; and a float pattern 13 bridging between these connector electrodes 35,36.
As shown in the FIG. 6, the first connector electrode 35, which is connected with the extended portion 51, is placed outside of contour of the scanning line 11 to avoid any overlapping with the scanning line 11. Reason for such placing is as follows; short circuit between the scanning line and the float pattern for storage capacity has been a problem as mentioned earlier; in view of this, it is natural to set a construction to avoid smaller yield due to the short circuit.
Such construction, however, results in a smaller aperture ratio by the extent of a space for the tandem repair circuit 6. In order for minimizing decrease of the aperture ratio, a gap between the extended portion 51-1 and the pre-scan-row pixel electrode 5-1 seems to be narrowed. However, in such case, there occurs a problem, after a patterning process for forming pixel electrodes, that etching residue may remain in the gap and may cause short circuit between the pixel electrodes.
Meanwhile, the array substrate in the prior art does not facilitate another kind of repairing—making the defected pixel as black in an array substrate for a normally white mode flat-pane display device. Such repairing is to be effected by short-circuiting the pixel electrode 5-1 paired with a defected TFT 9 onto the pre-scan-row scanning line 11-2.
In view of the above drawbacks, it is aimed to minimize decreasing of the aperture ratio resulted by placing the tandem repair circuit and in same time to prevent short circuit between pixel electrodes. In this case, matrix array substrate on subject is for flat-panel display device and has a tandem repair circuit, which is for connecting a storage-capacity-forming extended portion of a defected pixel electrode to next pixel electrode.
Further, it is aimed to facilitate a repair process of converting a luminous dot (bright defect) to a dark dot (unlit dot) when the matrix array substrate is for normally white mode flat-panel display device.